[feature request] Introduce experimental flag to ImageProcessor

[milasudril]

Summary

Introduce experimental flag to ImageProcessor that can be used to hide image processors that may change their iterface.

Motivation

When testing a new ImageProcessor, it would be a good idea to mark it as "experimental", so it is possible to change its interface without having the responsibility for breaking existing documents, which may rely on a particular interface.

Proposed solution

• Add static constexpr bool experimental() to ImageProcessor
• Add button to Image Processor Selector to show experimental ImageProcessors
• Update code generator. Experimental should be set to true by default

[milasudril]

It is probably a good idea to save that an ImageProcessor was experimental when a document was saved, and issue a warning when loading a document that was created with experimental image processors

[milasudril]

Also include Deprecated state, so it is possible to remove obsolete ImageProcessors. Use of deprecated image processors should also trigger a warning

[milasudril]

Checklist:

• [x] Introduce enum class ReleaseState:int{Experimental, Stable, Deprecated}
• [x] Add static constexpr ReleaseState releaseState() to ImageProcessor
• [x] Update code generator. If field not present, releaseState should return Experimental
• [x] Update GUI. By default only Stable, should be visible. Toggle buttons enable Experimental or Deprecated.
• [x] Mark all current ImageProcessors as stable
• [x] Denote that an ImageProcessor is Experimental when saving documents
• [x] Issue warning when loading ImageProcessor that whose state was saved as Experimental
• [x] Issue warning when loading ImageProcessor that was Deprecated

[milasudril]

Fixed